Acoustic telephone



(No Model.)

L. V. ELLIOTT.

ACOUSTIC TELEPHONE. No. 410,791. Patented Sept. 10, 1889.

UNITED STATES LARKIN V. ELLIOTT, OF

PATENT OFFICE.

MO ORESVILLE, INDIANA.

ACOUSTIC TELEPHONE.

SPECIFICATION forming part of Letters Patent No. 410,791, datedSeptember 10, 1889.

Application filed February 5, 1889. Serial No. 298,767. (No model.)

To aZZ whom it may concern:

Be it known that I, LARKIN V. ELLIOTT, a citizen of theUnited States,residing at Mooresville, in the county of Morgan and State of Indiana,have invented new and useful Improvem ents in Acoustic Telephones, ofwhich the following is a specification.

The invention relates to improvements in acoustic telephones; and itconsists in a certain novel construction and combination of devices,fully described hereinafter in connection with the accompanyingdrawings, and specifically pointed out in the appended claims.

In the drawings, Figure l is a perspective view of a receiver embodyingthe improvements. Fig. 2 is a central sectional view of the same. Fig. 3is a detail view of the diaphragm.

Referring by letter to the drawings, A designates the base of theimproved receiver, provided with a central opening 13, which is flaredtoward the front side of the base to a diameter of from three andone-half to about four inches, and over this enlarged end of the openingis stretched the diaphragm G, which is secured rigidly to the front sideof the base.

D represents the bell-shaped mouth-piece, which is attached to the frontside of the base, over the diaphragm, the bore thereof being about threeinches long. The bore of the mouth-piece is approximately parallelsidedfor the greater portion of its length, and substantially agrees indiameter with the small or rear end of opening B, and it is abruptlyflared at its extreme end to about four or four and one-half inches, orslightly larger than the large end of the opening 13, as shown in thedrawings.

I have found by experiment that much of the indistinctness, hollowness,and mm aturalness of the sound in acoustic telephones is caused, first,by the diaphragm being either too small or too large, and, second, bythe mouth-piece being too long and flared or enlarged gradually towardits free end. When the diaphragm is made about four and one -half inchesin diameter, so that about four inches is exposed, I have obtained thebest results; and when the mouthpiece is made in about the size andproportion described and flared at its end to about four and one-halfinches in diameter, the tone of the voice of the operator is preserved.It is neither hollow nor sharp, as when these proportions are notfollowed.

Another great disadvantage of telephones of this class is that thecontact of the wire or button with the diaphragm causes a roaring,singing sound, which interferes with the vibrations of the diaphragm andrenders the speech of the operator indistinct. Various devices haveheretofore been adopted with a View to overcoming this difficulty; butthey have been only partially successful.

In constructing the improved diaphragm I first stretch a sheet E ofthick rawhide very tightly across the opening of the base, preferablywhile wet, so that when it dries it will be still more tightly drawn. Ithen arrange a layer F of cotton batting or other soft fibrous materialon the rawhide. I then stretch a sheet G of thin rawhide over thebatting, but not so tightly as the first, and, lastly, I place a sheetll of velveteen on the front side of the loose sheet of rawhide.Theline-wire I passes through an opening in the center of the diaphragm,and is provided on its end with a button K, which bears against thevelveteen or other covering-sheet H.

It will thus be seen that the diaphragm consists of four members twosheets of stretched rawhide, (one being preferably heavier and tighterthan the other, forming an efficient backing) an interposed layer ofsoft fibrous material, and a covering of fabric which re ,ceives thepresure of the button. This covering may be omitted without entirelydefeating the object of the invention; but it is preferably used asdescribed, inasmuch as it aids materially in preventing the roaring andsin ging sound above referred to.

The combination of the layer or filling of soft fibrous material and thesheets of hide forms a cushion, which not only prevents the roaringsound in the receiver,but improves the sound by rendering the same moredistinct, and enables the diaphragm to reproduce a clear natural tone ofvoice, such as that which acts upon the diaphragm at the other end ofthe line-wire.

Having thus described the invention, I claim 1. In an acoustictelephone, a base-piece having a central transverse opening flaredtoward the front of the base, a mouth-piece mounted over the base andprovided with a bell-shaped bore agreeing in diameter 'at its front endwith the front or large end of the opening in the base and at its rearend with the smaller or rear end of the opening, and a diaphragminterposed between the front face of the base and the rear face of themouthpiece, and having contact with the latter face at all points exceptopposite its bore, substantially as specified.

2. The diaphragm for acoustic telephones, consisting of parallel sheetsof rawhide, which are held out of contact by an interposed filling orlayer of soft fibrous material, substantially as specified.

3. The diaphragm for acoustic telephones, having an innertightly-stretched sheet of rawhide, an outer loosely-stretched sheet ofrawhide, and an interposed filling or layer of soft fibrous material,substantially as specified.

4. The diaphragm for acoustic telephones, consisting of the sheets E Gof rawhide, the filling or layer of soft fibrous material interposedbetween the said sheets, and the covering H of fabric, substantially asspecified.

5. In an acoustic telephone, the combination, with the receiver, of thediaphragm consisting of the rawhide members E G, the filling or layer ofsoft fibrous material, and the I covering 0 of velveteen or fabric, andthe linewire extending through a central opening in the diaphragm andprovided with a button which bears on the said covering, substantiallyas specified.

In testimony that I claim the foregoing as my own I have hereto afiixedmysignature in presence of two witnesses.

- LARKIN V. ELLIOTT. Witnesses:

Orro E. ROOKER,

SAMUEL M. ROCKER.

